Abstract

The Hypothesis of Extended Cognition (HEC) holds that that not all human cognition is realized inside the head. The related but distinct Hypothesis of Extended Mentality (HEM) holds that not all human mental items are realized inside the head. Clark & Chalmers distinguish between these hypotheses in their original treatment of cognitive extension, yet these two claims are often confused. I distinguish between functionalist theories on which functional roles are individuated according to computational criteria, and those on which functional roles are individuated according to rational criteria. I then present an argument for a modest version of HEC from computational functionalism, based on Clark & Chalmers’ original argument. In doing so I articulate a successor to their parity principle, and review studies by Wayne Gray et al. that provide plausible evidence for actual cognitive extension. I then respond to a new criticism of HEC by Mark Sprevak using the modest account I have developed, arguing that Sprevak conflates HEC and HEM.